Rename tail to avoid clash with Base.tail

[cossio]

I typically import Base: tail into scope. If I then do using DataFrames, I get a warning

WARNING: using DataFrames.tail in module Main conflicts with an existing identifier.

Although Base.tail is not exported, it is documented (https://docs.julialang.org/en/v1/base/collections/#Base.tail) and I think many people use it regularly.

To avoid this clash, maybe DataFrames can use a different name for this function? Or it could just extend Base.tail.

[bkamins]

see #2262

[cossio]

@bkamins Any estimate of when this change will be released? I keep getting annoying bugs / warnings because of this (end up calling the wrong tail).

[bkamins]

Well - we could make a release now as we have enough functionality to justify it, but users wanted to postpone the release to make sure we include all breaking things in 0.22 and there are several loose ends related to select/transform/combine that need working out and might lead to breakage.

CC @oxinabox @nalimilan

[oxinabox]

I would really like hold off on release until we are done.
Its much easier to batch up upgrading literally dozens of packages.

[bkamins]

Just as a reference #2410 and #2314 (and related) are major pain points.